The present invention relates to a stator vane arrangement for rotating machinery in which stator vanes are arranged axially adjacent to rotor vanes.
In rotating machinery such as a gas turbine engine, stator vanes defining a plurality of nozzles are often arranged axially adjacent to rotor vanes. In such an arrangement, it is customary to select the solidity of each stator vane (axial dimension of the stator vane/circumferential gap between adjacent stator vanes) to be greater than a certain value so as to control the pressure loss by the stator vanes. It is typically accomplished by increasing the number of stator vanes so as to reduce the circumferential gap between adjacent vanes and reduce the axial dimension of each vane or increase the aspect ratio thereof (height of the trailing edge (h)/axial length at the hub (C)). A high aspect ratio means a slender stator vane.
However, increasing the number of stator vanes means an increase in the frequency of the oscillatory force that is produced by the stator vanes as the rotor vanes pass by the stator vanes in close proximity. To avoid a resonant vibration of the rotor vanes, it is necessary that the resonant frequency (xcfx89) of each rotor vane is adequately higher than the frequency (nN/60) of the external force produced by the stator vanes in relation with the rotor vanes.
Therefore, it is typically necessary to limit the number of stator vanes to avoid a resonant condition for being produced in the rotor vanes in a normal range of the rotational speed of the engine. Reducing the number of stator vanes necessarily requires the aspect ratio of each stator vane to be reduced. It is illustrated in FIG. 7. If the aspect ratio is 1 as indicated by the dotted line, the resonant condition is produced below the operating speed range (first mode) and within the operating speed range (second mode). On the other hand, if the aspect ratio is reduced to 0.32, the resonant condition is not produced as long as the engine rotation speed is within the operating range or lower. However, conventionally, reducing the aspect ratio causes a significant increase in the pressure loss by the stator vanes, and this necessitated a certain compromise in gas turbine engines.
In view of such problems of the prior art, a primary object of the present invention is to provide a stator vane arrangement for rotating machinery which allows the aspect ratio of each stator vane to be reduced so as to reduce the number of stator vanes without incurring an undesired pressure loss.
A second object of the present invention is to provide a stator vane arrangement for rotating machinery which allows the pressure loss by the stator vanes to be controlled.
A third object of the present invention is to provide a stator vane arrangement for rotating machinery which allows the resonant condition of the rotor vanes to be controlled by appropriately selecting the configuration of the stator vanes located immediately upstream of the rotor vanes.
A fourth object of the present invention is to provide a stator vane arrangement for rotating machinery which can provide a high performance while simplifying the fabrication process for the stator vanes.
A fifth object of the present invention is to provide a stator vane arrangement for rotating machinery which can provide a high performance while controlling the stress in the stator vanes.
According to the present invention, such objects can be accomplished by providing a stator vane arrangement including a plurality of stator vanes axially opposing a plurality of rotor vanes in rotating machinery, wherein: an aspect ratio of each stator vane as given as a ratio of a height of a trailing edge thereof to an axial length of a hub end thereof is 0.5 or less, and a tilt angle of a back surface of the stator vane at a trailing edge thereof with respect to a radial line is between 7 degrees and 42 degrees. The aspect ratio is more preferably approximately 3.0 for an optimum result.
Thus, by leaning or tilting each stator vane with respect to a radial line, the load acting on the hub end of each stator vane is reduced and a secondary flow is minimized. This contributes to the reduction in the pressure loss.
Preferably, a ratio of a distance between a trailing edge of each stator vane and a leading edge of the corresponding rotor vane to an axial length of the stator vane measured along a hub end of the vanes is 0.25 or smaller. By thus reducing the distance between a trailing edge of each stator vane and a leading edge of the corresponding rotor vane, the vortices that are produced immediately downstream of each stator vane are forwarded to the rotor vanes before they grow to any significant extent. This additionally contributes to the reduction in the pressure loss.